The invention relates to an internal combustion engine system comprising a combustor, a compressor arranged to compress air, an air guide arranged to guide compressed air from the compressor to the combustor, an expander arranged to expand exhaust gases from the combustor and to extract energy from the expanded exhaust vases, and an exhaust guide arranged to guide exhaust vases from the combustor to the expander. The invention also relates to an exhaust guiding unit an exhaust treatment unit and a vehicle.
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment, e.g. working machines. The invention can also be applied to cars. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle type.
It is known that internal combustion engines with multiple stages of compression and expansion may provide for reaching very high pressures and for extracting more energy from the fuel, U.S. Pat. No. 4,783,966A provides an example of such an engine. Such engines require however relatively large amounts of space, and may add weight to a vehicle in which they are provided.
It is desirable to reduce, tier vehicle propulsion applications, the space requirement and/or the weight of a multiple stage compression and expansion internal combustion engine.
According to an aspect of the invention, an internal combustion engine system comprising an internal combustion engine system is provided comprising
at least one combustor,
a compressor arranged to compress air,
an air guide arranged to guide compressed air from the compressor to at least one of the at least one combustor,
an expander arranged to expand exhaust gases from at least one of the at least one combustor and to extract energy from the expanded exhaust gases, and
an exhaust guide arranged to guide exhaust gases from at least one of the at least one combustor to the expander,
characterized in that the exhaust guide is at least partly integrated with the air guide.
It is understood that depending on the type of fuel system used for the engine, the compressor may be arranged to compress air only, or a premix of air and fuel.
Integrating the exhaust guide with the air guide provides for a combination of two parts which during engine operation present elevated pressures and temperatures. This in turn makes it possible to allow these guides to share loads generated by the operational conditions, so that the amount of material for these parts may be reduced. Hence weight may be saved. Also, the integration of the guides allows for a reduction of the space consumed by the engine. Therefore, both weight and space savings are provided, which is advantageous where the engine system is used in a vehicle.
The invention could be said to allow all of, or parts of the exhaust guide to be isolated by the air guide. This reduces the temperature of the wall material of the exhaust guide, which makes it possible to use less temperature resistant, and therefore cheaper material for the exhaust guide. Also, the isolation of the exhaust guide by the air guide provides for reducing the heat radiation around the exhaust guide, without the need to provide isolation material around the exhaust guide. This is a substantial advantage in vehicles, where space requirements are strict. The possibility to reduce or omit isolation material for the exhaust guide reduces the volume of the engine system, as well as the cost therefore.
In addition, the integration of the exhaust guide with the air guide allows the gas conducting volumes in the guides to share one or more walls. This in turn reduces energy losses of the gases when transported between the compressor(s), combustor(s) and expander(s).
In addition, the integration of the exhaust guide with the air guide allows for a movement of the compressed air in the air guide past the exhaust guide, providing an exchange of heat from the exhaust guide to the air. This heat exchange is augmented by the elevated absolute pressure in the air guide. The heat exchange provides for reusing the heat for power production, which may be of particular interest at a low load operation of the engine.
Thus, the invention provides an engine with multiple stages of compression and expansion with reduced weight and space requirements, and with reduced losses or improved efficiency.
Preferably, the exhaust guide comprises an integrated portion which is located within the air guide. Thereby, the exhaust guide is suitably arranged to penetrate an external wall of the air guide. The integrated portion of the exhaust guide being located within the air guide provides an advantageous manner of reducing the volume required for the engine system, e.g. in a vehicle. Also, material, and hence weight, can be reduced since the pressure difference across a wall of the integrated portion is reduced, thereby reducing the structural load and allowing less material to be used for the integrated portion. Also, the location inside the air guide provides a particularly advantageous way for the exhaust guide to transfer heat to the air in the air guide. In addition, the amount of insulation material surrounding parts of the engine system may be reduced since the air guide will provide insulation for the integrated portion.
Preferably, the integrated portion presents a wall delimiting the integrated portion, and that the integrated portion comprises an insulation layer located inside the wall. Thereby, the temperature in the material of said wall may be limited, so as to avoid a strength reduction in the material. This in turn allows less material to be used for said wall. Preferably, the integrated portion presents a circular cross section, which will further increase the structural integrity of the integrated portion, thereby allowing less material to be used for it.
The integrated portion may present a plurality of externally protruding flanges. Thereby, the beneficial exchange of heat to the compressed air moving past the integrated portion may be augmented.
Preferably, the air guide comprises an air buffer container arranged to provide an at buffer volume for the compressed air. Where the system comprises a plurality of combustors, the air buffer container may be arrange d to deliver the compressed air to a plurality of the combustors. Where the system comprises a plurality of compressors, the air buffer container may be arranged to receive compressed air from a plurality of the compressors. In alternative embodiments, there may be one or more air buffer containers, each dedicated for a single respective compressor and/or combustor.
The air buffer container reduces or eliminates a requirement in a multiple stage compression engine that the timing of inlet and outlet valves, for admission and ejection of air at the combustors and the compressors, must be highly correlated to avoid losses with pulsating flows. Thanks to the air buffer volume, this requirement of correlation of such valve timing may be relaxed without increasing the risk of pulsating flows. Thereby simpler and cheaper valve control systems may be employed,
It is understood that the air buffer volume of the air buffer container suitably presents a cross-section which is larger than any lateral cross-section, perpendicular to a local intended air flow direction, of air guide portions upstream and downstream of the air buffer volume.
Preferably, said at least part of the exhaust guide is located, within the air buffer container. Thereby, an advantageous use of a part of the air buffer volume for the integration of the at least part of the exhaust guide is provided, further augmenting the space saving benefits of the invention.
Preferably, the exhaust guide comprises an exhaust buffer container. Where the system comprises a plurality of combustors, the exhaust buffer container may be arranged to receive exhaust gases from a plurality of the combustors. Where the system comprises a plurality of expanders, the exhaust buffer container may be arranged to deliver exhaust gases to a plurality of the expanders. In alternative embodiments, there may be one or more exhaust buffer containers, each dedicated for a single respective combustor and/or expander.
The exhaust buffer container reduces or eliminates the risk of pulsating flows in the exhaust guide. Thereby simpler and cheaper valve control systems may be employed.
It is understood that the exhaust buffer container suitably presents a cross-section which is larger than any lateral cross-section, perpendicular to a local intended exhaust flow direction, of exhaust guide portions upstream and downstream of the exhaust buffer volume.
Preferably, the exhaust buffer container is located within the air guide. Advantageously, where the air guide presents and air buffer container as described above, the exhaust buffer container is located within the air buffer container. Thereby said risk of pulsating flows may be reduced or eliminated, while at the same time reducing the space requirements of presented by the exhaust buffer container and the air buffer container.
Preferably, a pre-expander exhaust treatment device is located in the exhaust guide, which pre-expander exhaust treatment device is arranged to provide an exhaust treatment process to the exhaust gases from the combustor. Thereby, the relatively high pressure and temperature between the combustor and expander may be advantageously utilised to support the processes in the exhaust treatment device. It should be noted however, that instead of housing an exhaust treatment device, the exhaust guide exhaust buffer container may be a pure buffer tank.
Preferably, where the exhaust guide comprises an integrated portion which is located within the air guide, the pre-expander exhaust treatment device is located in the integrated portion. Thereby, part of the heat generated by the processes in the exhaust treatment device may be advantageously transferred to the air in the air guide, with benefits as described above.
Preferably, the pre-expander exhaust treatment device comprises an oxidation catalyst, and/or a particulate filter. Where a particulate filter is provided in addition to an oxidation catalyst, the particulate filter may be located downstream of the oxidation catalyst. Thereby, the temperature increasing process of the oxidation catalyst may be used for advantageously elevating the heat in the particulate filter, increasing the efficiency of the latter. Also, particularly in diesel and high pressure gas injection (HPGI) engines, the risk of soot and catalyst coatings reaching the expander will be substantially reduced with said spatial arrangement of the oxidation catalyst and the particulate filter.
In some embodiments, the system comprises a post-expander exhaust treatment device arranged to receive exhaust gases from the expander and to provide an exhaust treatment process to the received exhaust gases. The post-expander exhaust treatment device may be a selective catalytic reduction (SCR) catalyst. This provides for a nitrogen oxide (NOx) reduction of the multi-stage expansion engine.
Preferably, the post-expander exhaust treatment device and the air guide are integrated with each other. Thereby the post-expander exhaust treatment device may be located within the air guide. Thereby, an advantageous heat exchange may be provided between the compressed air and the post-expander exhaust treatment device.
Preferably, where the exhaust guide comprises an integrated portion which is located within the air guide, the post-expander exhaust treatment device is located externally of the integrated portion and internally of an external wall of the air guide. Preferably, a pre-expander exhaust treatment device is located in the integrated portion, which pre-expander exhaust treatment device is arranged to provide an exhaust treatment process to the exhaust gases from the combustor. Thereby, and integration of the pre-expander exhaust treatment device and the post-expander exhaust treatment device may be provided, which may allow an advantageous heat transfer from the pre-expander exhaust treatment device to the post-expander exhaust treatment device. This is particularly advantageous, since the first expander extracts energy, i.e. heat from the exhaust gases, and by the heat transfer from the pre-expander exhaust treatment device, the temperature in the post-expander exhaust treatment device may be kept high enough for the process therein. Further, the post-expander exhaust treatment device may provide an insulation of the pre-expander exhaust treatment device
Said expander may be a first expander, wherein the system also comprises a second expander arranged to receive and expand exhaust gases from the post-expander exhaust treatment device and to extract energy from the expanded exhaust gases. The second expander may extract energy provided by the heat production of the process in the post-expander exhaust treatment device. The second expander may be a piston expander arrange to drive a crankshaft of the engine system with the extracted energy.
The system is, preferably arranged so that during an operation thereof, the post-expander exhaust treatment device presents a pressure within the range of 4-8 bar, and a temperature within the range of 250-400° C. Thereby, advantageous conditions are provided for the processes in the post-expander exhaust treatment device. However, in some embodiments, the post-expander exhaust treatment device may be located in a tailpipe of a vehicle in which the engine system is provided. Thereby, the post-expander exhaust treatment device may present during an operation of the engine system a pressure of around 1 bar, and a temperature within the range of 200-300° C.
Preferably, the system is arranged so that during an operation thereof, the exhaust guide presents a pressure within the range of 10-25 bar. Such a high pressure makes it possible to provide the exhaust guide with an oxidation catalyst and/or a particulate filter presenting small volumes, which is favourable for limiting the overall size of the engine system. Also, the high absolute pressure provides for a very small pressure drop over the pre-expander exhaust treatment device. The combination of the location of the pre-expander exhaust treatment device and said temperature and pressure ranges provides for a very small decrease in engine efficiency compared to traditional exhaust after treatment systems in vehicle tail pipes.
Preferably, the system is arranged so that during an operation thereof, the exhaust guide presents a temperature within the range of 300-950° C., preferably 500-900° C. It is understood that the temperature within such a range may vary depending on the operational situation of the engine system. It should be noted that such a temperature range provides very favourable conditions for a particulate titter in the exhaust guide for continuous oxidation of soot, so that the pre-expander exhaust treatment device may be provided without any catalyst. Said temperature range may also be beneficial for catalytic, methane oxidation, e.g. in a high pressure gas injection (HPGI) engine.
The system may arranged so that during an operation thereof, the air guide presents a pressure within the range of 8-12 bar, and/or a temperature within the range of 250-350° C. Thereby, a high power output of the engine, with an effective combustion may be provided.
The invention is particularly advantageous where the combustor comprises a piston arranged to reciprocate in a cylinder, and to drive a crankshaft of the system. It is understood that the system may comprise a plurality of combustors, each comprising a piston arranged to reciprocate in a respective cylinder, whereby the piston are all arranged to drive the crankshaft. The compressor is preferably a piston compressor, arranged to be driven by the crankshaft. The expander is preferably a piston expander arranged to drive the crankshaft with the extracted energy. Thus, the invention may be advantageously implemented in a multistage compression and expansion engine where the compressors) and the expander(s) are connected to the crankshaft. Such a connection may be direct or indirect, as exemplified below. Typically, the expander(s) may provide 30-50%, e.g. 40%, of the total power of the engine, and the compresser(s) may take 10-20% of the total power of the engine.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.